1. Field of the Invention
This invention relates to a low cost polyurethane elastomer having high resilience and shear resistance useful in the manufacture of golf ball covers.
2. Description of Related Art
Polyurethane elastomers are well known and can be formed by reacting a diisocyanate, e.g., diphenyl methane diisocyanate (MDI), toluene diisocyanate (TDI), isophorone diisocyanate (IPDI), and the like, with an organic polyol, e.g., polytetramethylene ether glycol (PTMEG), polyester or polycaprolactone glycol (PE), homopolymers and copolymers of ethylene oxide and propylene oxide (E/PO), and the like, and a chain extender, e.g., an aliphatic diol, such as, 1,4 butanediol (BD), or an aromatic diamine, such as, diethyltoluene diamine (DETDA). Catalysts, such as, triethylene diamine (TEDA), can be used to increase the reactivity of the components. Additional components, such as, UV stabilizers, antioxidants, dyes, antistatic agents, and the like, can be added, if desired.
U.S. Pat. No. 3,147,324 discloses a method of covering a golf ball with a liquid urethane polymer by suspending the golf ball center within a mold cavity and filling the mold cavity with the liquid polymer.
U.S. Pat. No. 3,979,126 discloses a solid plastic polyurethane golf ball. The golf ball comprises a polyether urethane prepolymer with a curing agent.
U.S. Pat. No. 4,061,662 describes a process which is effective in removing unreacted tolylene diisocyanate (TDI) from a polyisocyanate by bringing said polyisocyanate into contact with molecular sieves.
U.S. Pat. No. 4,123,061 discloses a polyurethane golf ball comprising a core and a cover at least one of which is a polyether urethane prepolymer with a curing agent selected from the group consisting of trifunctional polyols, tetrafunctional polyols and amine-type curing agents having at least two reactive amine groups.
U.S. Pat. No. 4,182,825 discloses capping hydroxy terminated polyethers with toluene diisocyanate, and substantially reducing the amount of unreacted toluene diisocyanate. When cured with 4,4'-methylene-bis-(2-chloroaniline), the cured products are said to have superior dynamic properties to the corresponding toluene diisocyanate capped polyethers with the usual unreacted toluene diisocyanate content. The cured products are said to be useful in fabricating industrial tires.
U.S. Pat. No. 4,288,577 discloses the reaction of a large excess of 1,4-butanediol with methylenebis (4-phenyl isocyanate) to give a mixture of urethanediols which is a suitable curing agent for isocyanate-terminated polyurethane prepolymers, especially prepolymers made from methylenebis (4-phenyl isocyanate) and polyols. It is said to be desirable to have a urethanediol mixture in which at least about 88 weight percent consists of the reaction product of 2 moles of 1,4-butanediol with 1 mole of the diisocyanate, about 10 weight percent of the reaction product of 3 moles of 1,4-butanediol with 2 moles of the diisocyanate, and no more than about 2 weight percent of 1,4-butanediol. The cured polyurethanes are said to have higher hardness and better overall physical properties than methylenebis-(4-phenyl isocyanate)-based polyurethanes cured with conventional commercial diols providing "hard" cured products.
U.S. Pat. No. 4,294,951 discloses rapidly cured polyurethane elastomers that are prepared by mixing a diphenylmethanediisocyanate based liquid prepolymer obtained from polytetramethylene ether glycol and an aliphatic diol at specified proportions, and a curing agent essentially containing said polytetramethylene ether glycol, diol and organometallic catalyst.
U.S. Pat. No. 4,385,171 discloses removing unreacted diisocyanate from a polyurethane prepolymer reaction product mixture by co-distillation of the unreacted diisocyanate with a compound which is at least partially miscible with the prepolymer and which boils at a temperature greater than the boiling point of the diisocyanate. A highly efficient removal rate is said to be achieved in that the concentration of unreacted diisocyanate remaining in the reaction product mixture is generally less than about 0.1 percent, and in many cases less than about 0.05 percent, based on the weight of the prepolymer.
U.S. Pat. No. 4,555,562 discloses a polyurethane elastomer product formed by curing a mixture of an NCO terminated urethane prepolymer and a polyhydroxyalkylphosphine oxide.
U.S. Pat. No. 4,631,298 discloses mixtures of aromatic diamines, polyurethanes made therefrom, and processes for the preparation of the polyurethanes. The mixtures of aromatic diamines comprise a first aromatic diamine having a machine gel time of about 1 to 4 seconds in a 50,000 psi modulus RIM formulation reaction and the second aromatic diamine having a slower machine gel time of about 1.5 to 15 times that of the first aromatic diamine. The mixtures provide gel times of about 2.5 to 10 seconds, suitable for filling large molds such as automotive body panels. The aromatic diamine mixtures allow use of larger proportions of diamine to provide polyurethanes that are said to be rigid but not brittle at demold and have unexpectedly superior flexural modulus properties. The polyurethanes formed with the chain extender mixtures are also said to have flexural modulus superior to polyurethanes formed from either of the diamines individually.
U.S. Pat. No. 4,888,442 is directed to a process for reducing the free monomer content of polyisocyanate adduct mixtures wherein the adduct has an average isocyanate functionality of greater than about 1.8 which comprises treating the polyisocyanate adduct mixture in the presence of 2 to about 30 percent by weight of an inert solvent, based on the weight of the polyisocyanate mixture, in an agitated thin-layer evaporator under conditions sufficient to reduce the free monomer content of the polyisocyanate adduct mixture below that level which is obtainable in the absence of a solvent.
U.S. Pat. No. 5,334,673 discloses a golf ball made from a composition of a polyurethane prepolymer and a slow-reacting polyamine curing agent and/or a difunctional glycol. The slow-reacting polyamine curing agents and difunctional glycols are 3,5-dimethylthio-2,4-toluenediamine; 3,5-dimethylthio-2,6-toluenediamine; N,N'-dialkyldiamino diphenyl methane; trimethyleneglycol-di-p-aminobenzoate; polytetramethyleneoxide-di-p-aminobenzoate; 1,4-butanediol; 2,3-butanediol; 2,3-dimethyl-2,3-butanediol; ethylene glycol; and mixtures thereof.
U.S. Pat. No. 5,387,750 discloses a method for producing an in-mold coated plastic article having an adherent coating wherein the coating composition is said to have improved surface coverage properties and a fast cure rate. The coating composition contains (a) a first component comprising at least one polyol having at least 4 hydroxyl groups and a viscosity at room temperature of 6000 cps or less; and (b) a second component comprising a solvent-free isocyanate prepolymer. The viscosity of the coating composition is 15000 cps or less at room temperature.
U.S. Pat. No. 5,599,874 discloses a thermoplastic polyurethane elastomeric seal composition comprising, by weight, about 90% to 99% thermoplastic polyurethane elastomer and about 1% to 10% fibers. Also, the thermoplastic polyurethane elastomer is derived from the reactants comprising: (i) a mixture of polyol and an aromatic chain extender in a molar ratio in the range of from about 40:60 to about 60:40 of butanediol glycol adipate to hydroquinone bis 2-hydroxyethyl ether, and (ii) 1,5 naphthalene diisocyanate present in a molar ratio in the range of about 50:50 to about 54.5:45.5 of 1,5 naphthalene diisocyanate to the said first mixture of polyol and an aromatic chain extender. After curing, the thermoplastic polyurethane elastomeric seal compound is said to have outstanding wear resistance and low compression set.
U.S. Pat. No. 5,692,974 relates to methods of using cationic ionomers in golf ball cover compositions and to golf balls which have covers and cores that incorporate urethane ionomers. The polyurethane golf ball cover is said to have improved resiliency and initial velocity through the addition of an alkylating agent such as t-butyl chloride to introduce ionic interactions in the polyurethane and thereby produce cationic type ionomers.
U.S. Pat. No. 5,703,193 discloses a process for reducing the amount of residual organic diisocyanate monomer in a polyurethane prepolymer reaction product mixture which comprises distilling the polyurethane prepolymer reaction product mixture in the presence of a combination of at least one inert first solvent with a boiling point below the boiling point of the residual organic diisocyanate monomer and at least one inert second solvent with a boiling point above the boiling point of the residual organic diisocyanate monomer, at a temperature which exceeds the vaporization temperature of the residual organic diisocyanate monomer and which is below the decomposition temperature of the polyurethane prepolymer.
U.S. Pat. No. 5,733,428 discloses a method and apparatus for making a golf ball having an encapsulated core or a non-treated core and a polyurethane cover of selected composition in which equipment is employed for aligning, centering and locating the core in relationship with the molding of the cover thereon.
U.S. Pat. No. 5,849,168 discloses a method of applying a coating material to an outer surface of a golf ball, the method comprising molding a golf ball having an outer dimpled surface under a pressure greater than ambient pressure within a mold cavity; formulating a golf ball coating composition; introducing a sufficient amount of the coating composition into the mold cavity between the golf ball outer surface and an inner surface of the mold cavity to substantially surround and coat the entire outer surface of the golf ball; curing the coating composition upon the ball outer surface and removing the coated ball from the mold cavity.
U.S. Pat. No. 5,885,172 is directed towards a multilayer golf ball which comprises a core, an inner cover layer and an outer cover layer, wherein the outer cover layer comprises a thermoset material formed from a castable, reactive liquid, said outer layer having a thickness of less than 0.05 inch and said inner cover layer comprising a high flexural modulus material.
U.S. Pat. No. 5,908,358 discloses a golf ball cover produced from a composition comprising an isocyanate-functional prepolymer and a curing agent of a polyamine or glycol, and an organic compound having at least one epoxy group such as the diglycidyl ether of bisphenol A.
U.S. Pat. No. 5,929,189 discloses a golf ball that comprises a core and a cover enclosing the core. The cover resin is composed mainly of a thermoplastic polyurethane elastomer having an aliphatic diisocyanate component and exhibiting a tan .delta. peak temperature of not higher than -20.degree. C. in viscoelasticity measurement.
U.K. Pat. No. 1,101,410 discloses a prepolymer obtained by reacting a larger-than-usual excess of diisocyanate with glycol (either polyether or polyester type) and then removing substantially all of the unreacted diisocyanate from the crude prepolymer before the latter is contacted with a curing agent.
WO 98/37929 discloses a composition useful for golf ball covers that comprises a blend of a diisocyanate/polyol polyurethane prepolymer with a curing agent comprising a blend of slow-reacting diamine with a fast-reacting diamine such as dimethylthio 2,4-toluenediamine and diethyl 2,4-toluenediamine, respectively. A golf ball cover made with this composition is said to exhibit the characteristic feel and playability of a balata cover with superior durability characteristics (cut and shear resistance) which exceed those of a balata or ionomer cover.
Polyurethanes are currently used in the manufacturer of golf ball covers such as those on the Maxfli Revolution and the Titleist Professional. As indicated in U.S. Pat. No. 5,334,673, polyurethanes are advantageous in the production of golf ball covers because they have the feel and click of balata covered balls with much greater cut resistance. In addition, the polyurethanes are generally more resilient than balata, allowing balls to be made with both good feel and good distance. Resilience can be measured as percent rebound of a steel ball bouncing on a flat elastomer sample from a height of one meter, where the sample is at least 0.5 inch thick and is firmly mounted so as to prevent movement. A good golf ball cover material should have at least 40% reilience as measured on this test. Ionomer covers have good resilience, but are harder and do not give the click and feel of the polyurethane and balata covers.
Another advantageous feature of polyurethane formulations is shear resistance, as indicated in U.S. Pat. No. 5,908,358. Shear resistance measures the damage to a cover from the impact of a club with sharp grooves, which can tear away bits of the cover. In contrast, cut resistance measures the resistance to damage of the cover from a mishit shot, where the leading edge of the iron cuts directly into the cover. Shear resistance of polyurethane formulations vary, and the method of U.S. Pat. No. 5,908,358 is one method that can be used to improve the shear resistance of a polyurethane formulation.
Although polyurethane formulations are now known that give both shear resistance and acceptable resilience, while maintaining the click and feel of balata, the cost of such formulations is reasonable only for higher priced golf balls. Lower priced balls that require lower cost raw materials continue to be made with the less expensive ionomer covers. It would be advantageous if a polyurethane formulation could be prepared for significantly reduced cost without compromising shear resistance, resilience, and feel.
PTMEG, the use of which has been disclosed in a number of patents, is often chosen as the polyol in golf ball cover formulations. A paper on polyurethane elastomer selection, titled "What Polyurethane, Where?", and presented to the Polyurethane Manufacturer's Association in May, 1982, indicates that the three main polyol classes are high cost PTMEG ethers, low cost E/PO ethers, and esters. Esters are generally not suited to applications requiring resilience, since they have the lowest rebound. On the other hand, the high cost ethers, and particularly MDI ethers have high resilience, making them an acceptable choice. The low cost E/PO ethers have the lowest tear strength and abrasion resistance, and are generally used for low performance applications. This does not make them a prime candidate for golf ball cover evaluation, where shear and cut resistance are important. They have generally been dismissed as potential candidates.
The polyol can be used directly in the reaction mixture, or pre-reacted with diisocyanate to form a prepolymer before the addition of a chain extender, or both. While the prepolymer process is generally preferred, it is often desirable to use some of the polyol directly in the reaction mixture. This allows for adjustment of formulation hardness by adjusting the amount of polyol and chain extender in the formulation, and alleviates the need to use a different prepolymer when a different hardness in needed.
In preparing a polyurethane prepolymer, the organic diisocyanate monomer is employed in a stoichiometric excess of the diisocyanate monomer in relation to the polyol (an NCO:OH ratio greater than 1:1, usually about 2:1 or greater). The use of such an excess of diisocyanate monomer, however, results in an undesirable amount of unreacted volatile diisocyanate monomer in the prepolymer reaction product mixture. While some polyurethane processors have ventilation equipment capable of handling these volatile monomers, others have insufficient ventilation and require the use of a low free monomer prepolymer.
Several techniques have been described in the art as useful for reducing the amount of diisocyanate monomer in the prepolymer reaction product mixture. For example, U.K. Patent No. 1,101,410 and U.S. Pat. No. 4,182,825 describe a process for distilling the prepolymer reaction product under vacuum conditions to reduce the amount of diisocyanate. U. S. Pat. No. 4,061,662 describes a process for the removal of unreacted toluene diisocyanate from prepolymers by passing the prepolymer reaction product through a column containing a molecular sieve. U.S. Pat. No. 4,385,171 describes a method for the removal of unreacted diisocyanate from polyurethane prepolymers by codistilling the prepolymer reaction product with a compound that boils at a temperature greater than the boiling point of the diisocyanate. U.S. Pat. No. 4,888,442 describes a two-step process consisting of a first step of distilling the prepolymer reaction product to remove the bulk of the diisocyanate and then, in the second step, adding a solvent to the distilled prepolymer reaction product and passing the resultant mixture through an agitated thin-film evaporator. According to this patent, the vaporization temperature of the solvent should be exceeded under the conditions employed in the thin layer evaporator. U.S. Pat. No. 4,288,577 describes the removal of unreacted methylene bis(4-phenyl isocyanate) (MDI) via solvent extraction with hexane.
The procedures described above relate to reduction of such diisocyanate compounds as toluene diisocyanate (TDI), methylene-bis-(4-phenyl)isocyanate (MDI), and the like. Other diisocyanate monomers with high melting points, such as para-phenylene diisocyanate (PPDI), can be removed by the process of U.S. Pat. No. 5,703,193, which comprises distilling the polyurethane prepolymer reaction product mixture in the presence of a combination of at least one inert first solvent with a boiling point below the boiling point of the residual organic diisocyanate monomer and at least one inert second solvent with a boiling point above the boiling point of the residual organic diisocyanate monomer, at a temperature that exceeds the vaporization temperature of the residual organic diisocyanate monomer and that is below the decomposition of the polyurethane prepolymer.